<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    body{
      margin: 0;
      padding: 0;
      background-image: url(../images/grid.png);
    }
    canvas{
      background-color: rgba(255, 0, 0, 0.1);
    }
  </style>
</head>
<body>

  <canvas id="tutorial" width="300" height="300px">
    你的浏览器不兼容Canvas,请升级您的浏览器!
  </canvas>

  <script>
    window.onload = function() {
      let canvasEl = document.getElementById('tutorial')
      if(!canvasEl.getContext){
        return
      }
      let ctx = canvasEl.getContext('2d') // 2d | webgl
    

      ctx.lineWidth = 10
      ctx.lineCap = 'butt' // butt round square
      ctx.lineJoin = 'bevel' // miter  round  bevel
      
      ctx.beginPath()
      ctx.moveTo(0, 0)
      ctx.lineTo(100, 100)
      ctx.lineTo(200, 0)
      ctx.stroke()

      
    }
  </script>
</body>
</html>